Currently, when people search and develop lead-free or low lead free-cutting brass alloys, they typically follow two routes to find the elements which could replace Lead: one route is to select the elements which hardly form solid solutions in Cu and can't form intermetallic compounds with Cu, such as Bi, Se and Te, etc; the other route is to select the elements which will form solid solutions in Cu wherein the solid solubility is reduced with decreasing temperature, so as to form intermetallic compounds with Cu, and with Sb, P, Mg, Si, B and Ca, etc. The first route has been well-known for some time. The second route is a more recent development.
In the process of researching and developing, considering the process properties, and comparing properties versus market cost requirements, the selection of elements for an alloy, and their range, will vary. Therefore, varied lead-free free-cutting brass alloys have been invented The bismuth brass alloy invention is the most common of these alloys.
For example, Pub. No. CN101225487A to Xuhong Hu discloses an arsenic-containing low-lead brass alloy which comprises (wt %) 57-62 Cu, 36-43 Zn, 0.01-1.0 Al, 0.05-2.5 Bi, 0.005-0.3 As, ≦0.2 Pb and ≦0.65 Sn, wherein small amounts of Ni, Fe and S and minimum amounts of Si, Mg, Mn and Re (Rhenium) are selectively added. No P is added. Arsenic is one of the main elements of such an alloy. If its As content is in the middle to upper limits of the above-specified range, and if the content of Pb is in the range of 0.1-0.2 wt %, then both As and Pb are released into the water in amounts that will exceed the upper limits of the NSF standard. Therefore, such brass alloys cannot be used in the components for drinking water supply systems, such as faucets and valves.
Pat. No. CN1045316C to Kohler discloses a low-lead bismuth brass alloy which comprises (wt %) 55-70 Cu, 30-45 Zn, 0.2-1.5 Al, 0.2-0.3 Bi, ≦1.0 Pb, ≦2.0 Ni, ≦1.0 Fe, ≦0.25 In, and 0.005-0.3 Ag, further comprising minimal amounts of one or more of the elements Ta, Ga, V, B, Mo, Nb, Co, and Ti. Zr is selectively added. No Si or P is added.
Pub. No. CN1710126A to Powerway discloses a lead-free free-cutting low-antimony bismuth brass alloy and its manufacturing method which comprises (wt %) 55-65 Cu, 0.3-1.5 Bi, 0.05-1.0 Sb, 0.0002-0.05 B, wherein elements such as Ti, Ni, Fe, Sn, P and rare earth elements are selectively added and the balance is Zn and impurities. No Si or Al is added. If the content of Sb is ≧0.1, the amount of Sb released in the water will exceed the requirements of the NSF standard.
JP2000-239765A to Joetsu discloses a lead-free brass alloy with corrosion resistance for castings, which comprises (wt %) 64-68 Cu, 1.0-2.0 Bi, 0.3-1.0 Sn, 0.01-0.03 P, 0.5-1.0 Ni, 0.4-0.8 Al, <0.2 Fe and the balance being Zn and impurities. The content of Bi is higher and no Si is added.
With the increasingly extensive application of bismuth brasses, their negative effects are also increasingly notable, such as susceptibility to hot and cold cracking, poor weldability, the necessity to slowly heat and cool when annealing, etc. The cause of these negative effects has a common thermodynamic reason: the large differential between the surface tension of bismuth (350 dyne/cm) and that of copper (1300 dyne/cm), and the fact that bismuth cannot form a solid solution in copper and cannot form intermetallic compounds with copper. As a result, liquid bismuth has good wetting with α and β grains of copper and brass. The dihedral angle between bismuth and copper or brass tends to zero. After solidification, bismuth is distributed in the grain boundary in the form of a continuous film.
Nowadays, the developed bismuth brasses are mainly deformation alloys and comprise more than 0.5 wt % bismuth. The public casting bismuth brasses, such as C89550 (which comprises 0.6˜1.2 wt % Bi), have high tendencies to experience hot cracking during low pressure die casting, and are not easily welded.
Lead-free or low-lead free-cutting antimony brass has excellent castability, weldability, hot working formability, and dezincification corrosion resistance. However, antimony is more toxic than lead. The NSF/ANSI61-2007 standard requires that Sb is released in drinking water in amounts ≦0.6 m/L and that Pb is released in amounts ≦1.5 m/L (NSF61-2005 requires that Pb release is ≦5 μg/L). Antimony brass is not suitable for components used in drinking water supply system.
Lead-free free-cutting silicon brass is a brass which has certain good developing prospects. Currently researched and developed lead-free free-cutting silicon brasses are mainly low-zinc deformation silicon brass. Most of them comprise small amounts of bismuth and the cost of raw material is rather higher.
Aluminum brass has good corrosion resistance, but its cuttability is inadequate. Few patents and other literature exists relating to lead-free free-cutting aluminum brasses. U.S. Pat. No. 3,773,504 (1973) discloses a Cu—Zn—Al—P series alloy having wear resistance. Japanese Patent 2003-253358 discloses a lead-free free-cutting low-zinc aluminum brass (containing vanadium and boron, etc.)